1. Field of the Invention
The present invention relates to the preparation of a water-soluble table capable of dissolving without residual particulate matter.
Active ingredients, e.g., pharmacologically active compounds, confectionary products and standards for calibration devices, can be conveniently and economically fabricated into tablets. In order to enable the incorporation of an active ingredient into a tablet, the tablet formulation must have certain characteristics; the ability to flow freely, cohesiveness and lubricity. Because many active compounds do not possess these characteristics, methods of tablet formulation include the incorporation of inert materials known as "additives". These additives include compounds which help to impart satisfactory characteristics to the tablet formulation and include compounds which function as diluents, binders and lubricants.
Diluents include compounds such as dicalcium phosphate, calcium sulfate, lactose, kaolin, mannitol, sodium chloride and powdered sugar. Binders impart cohesiveness to tablet formulations and include compounds such as starch, gelatin, sugars and gums. Other binders include polyethylene glycol, waxes and ethylcellulose.
Lubricants improve the rate of flow, prevent adhesion of the tablet material to the surface of the dies and punches, and reduce "static" and interparticle friction. During mixing or compressing of the formulation, or during ejection of the tablet from the die, an undesirable static charge may occur. Examples of lubricants suggested in the prior art are magnesium stearate, calcium stearate, talc, polyethylene glycol and sodium lauryl sulfate.
Generally two methods are used in table formulation; the wet granulation method and the dry granulation method. The wet granulation method usually involves mixing together the active ingredient, along with a diluent. Solutions of a binding agent are added to form a "wet" mixture. The mixture is then dried, a dry lubricant added, and the mixture compressed into a tablet.
The dry granulation method usually involves mixing together the active ingredient and, if required, a diluent, and part of the lubricant. The mixture is granulated and the remaining lubricant added, blended, and the mixture compressed into tablets.
The simplest tableting machines available are those having the single-punch design. Formation of a tablet on a single-punch tablet press is accomplished as described below. Single punch tablet presses are operated by filling a feed shoe with the tablet composition and emptying the feed shoe into a die cavity. The feed shoe is retracted and scrapes all excess composition away from the die cavity. An upper punch compresses the granulation within the die cavity. After compression, the upper punch retracts and a lower punch rises and ejects the tablet. As the feed show returns to fill the die cavity, it pushes the compressed tablet from the die.
As the name indicates, water-soluble tablets contain various soluble components. It is important for aesthetic reasons that complete dissolution occur, and that no particulate residue or visible foam remain after the tablet is dissolved.
In the process of manufacturing water-soluble tablets, the prior art lubricants such as magnesium and calcium stearate, talc, polyethylene glycol and sodium lauryl sulfate each have disadvantages. The stearates and talc are relatively insoluble and tend to inhibit the rate of dissolution of the water-soluble tablet and cause the resulting solution to appear cloudy because of the presence of undesirable particulate residue. Polyethylene glycol has an undesirably low melting point, while sodium lauryl sulfate can produce excessive foam when the water-soluble tablet is dissolved, which may remain visible on the solution surface.
2. Description of the Prior Art
U.S. Pat. No. 3,692,896 describes the preparation of a water-soluble tablet produced by a process designated as "direct compression" of the active ingredient. Direct compression involves compressing tablets directly from powdered material with the use of only a small amount of additives, e.g., diluents or lubricants. The patent teaches the use of super micro particulate powder of polyethylene glycol having a particle size of less than 50.mu., preferably 1-10.mu. and 1-5.mu..